Achieving ultrahigh electrochemical performance by surface design and nanoconfined water manipulation

The effects of nanoconfined water and charge storage mechanism are crucial in achieving ultrahigh electrochemical performance of two-dimensional (2D) transition metal carbides (MXenes). We propose a facile method to manipulate the nanoconfined water through surface chemistry modification. By introducing oxygen and nitrogen surface groups, more active sites were created for Ti3C2 MXene, also with the interlayer spacing significantly increased by accommodating three-layer nanoconfined water. Exceptionally high capacitance of 550 F g–1 (2000 F cm–3) was obtained with outstanding high-rate performance. The atomic scale elucidation of layer-dependent properties of nanoconfined water and pseudocapacitive charge storage was deeply probed through a combination of ‘computational and experimental microscopy’. We believe the understanding and manipulation strategy of nanoconfined water will shed light on pushing MXene and other 2D materials to better electrochemical performance.